operon

The lac-operon consists of a operator, gene Z, gene Y, and Gene A.

The repressor protein will be able to bind onto the operator side. After binding onto the operator side, the RNA polymerase will not be able to proceed to read the DNA, and therefore, the DNA will not be transcripted.

In order for the RNA polymerase to be able to transcript the DNA, the lactose will bind onto the repressor, and therefore changing the shape of the repressor, and it will no longer be able to fit onto the operator.

After that, the RNA polymerase is able to proceed into transcripting the DNA without any obstacle blocking.

After transcription, it will form mRNA, and then it will form protein. The gene A codes for beta-galactosidase, which is able to break down lactose to form glucose.

DNA Folding (School revision)

1) Firstly, the long strand double helix DNA coil a few rounds around the octomer histones. The octomer histones are positively charged.

2) In order to stabilise the DNA being uncoiled from the octomer histone, another protein called the H1 histone will attached onto the DNA and the octomer like a scotch tape, to stabilise it. The ending product is called nucleosome.

3) DNA continued to form more and more nucleosomes. After that, these nucleosomes in a long chain will coil itself like a spring shape. It will then be known as solenoid.

4) The solenoid then attach to another protein called scaffold to form loops. That is called the loop solenoid.

5) It then made up into chromosomes.

(WARNING: Information may be incorrect. If there are any incorrect information, or anything more to add, please give comments. )

DNA Replication (MCB school revision)

Okazaki fragment - short fragment of DNA.

Helicase - separates the double strand.

Single-strand binding protein – prevents single strand coiling back to original shape.

DNA Polymerase synthesize only 5’ to 3’.

5’ to 3’ (direction of DNA polymerase) = Leading strand (3’ to 5’ old strand, 5’ to 3’ new strand, direction towards helicase)

5’ to 3’ (direction of DNA polymerase) = Lagging strand (5’ to 3’ old strand, 3’ to 5’ new strand, direction away from helicase)

Leading strand –

1) RNA Primase - attach a RNA Primer onto the strand
2) DNA Polymerase 3 - adds deoxyribonucleotides to synthesize the new complementary strands of DNA.

Lagging Strand –

1) RNA Primase – attaches a RNA Primer
2) DNA Polymerase III - adds deoxyribonucleotides
3) DNA Polymerase I – removes the RNA and replace it with DNA
4) DNA ligase – Forms phosphodiester bonds

Molecular and Cell Biology (School revision) - Transcription and translation

In order to undergo the central dogma, the DNA has to undergo transcription and translation.

In transcription, the RNA Polymerase splits the double strand into a single strand. The RNA Polymerase will then bring the nucleotides, and then the nucleotides will firstly find the start codon. After finding the start codon, the RNA Polymerase will then begin to bind the nucleotides to form a single strand. As the RNA Polymerase moves along to form a longer RNA strand, the front part of the mRNA will detached from the single strand, and after the RNA Polymerase reaches the stop codon, the mRNA strand will be formed.

The mRNA strand will then move out of the nucleus to the cytoplasm, and then translation will occur.

For translation, firstly, the ribosome will bind onto the mRNA strand, and then it will also find the start codon. After it found the start codon AUG, it will then start to read.

As it moves along, the tRNA with the anti-codon on the other side will then bind onto the codon. On the other end, it has the amino acid. As the ribosome moves along, there will be more tRNA binding onto the codon.

As the ribosome moves along, the tRNA on the front part will started to detached with the mRNA strand, and leaving behind the amino acid. The ribosome will also help to form the peptite bond of the amino acid.

After the ribosome reaches the end codon, the amino acid will then be formed.

In order to form protein, there will be more amino acids formed, which will then made up proteins.